Method and apparatus for system information acquisition, beam failure recovery and cell reselection

ABSTRACT

The disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT). The disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. An apparatus, a method and a system for system information acquisition, beam failure recovery, and cell reselection in wireless communication system are provided.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based on and claims priority under 35 U.S.C. §119(e) of a U.S. Provisional application Ser. No. 62/732,168, filed onSep. 17, 2018, in the U.S. Patent and Trademark Office, the disclosureof which is incorporated by reference herein in its entirety.

BACKGROUND 1. Field

The disclosure relates to a wireless communication system. Moreparticularly, the disclosure relates to an apparatus, a method and asystem for system information acquisition, beam failure recovery andcell reselection in wireless communication system.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of fourth generation (4G) communication systems, efforts havebeen made to develop an improved fifth generation (5G) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘Beyond 4G Network’ or a ‘Post Long Term Evolution(LTE) System’. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), Full Dimensional MIMO(FD-MIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud Radio Access Networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,Coordinated Multi-Points (CoMP), reception-end interference cancellationand the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) andsliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), and filter bank multi carrier (FBMC), non-orthogonalmultiple access (NOMA), and sparse code multiple access (SCMA) as anadvanced access technology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof Things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofEverything (IoE), which is a combination of the IoT technology and theBig Data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “Security technology” have been demanded forIoT implementation, a sensor network, a Machine-to-Machine (M2M)communication, Machine Type Communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing Information Technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies such asa sensor network, Machine Type Communication (MTC), andMachine-to-Machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RadioAccess Network (RAN) as the above-described Big Data processingtechnology may also be considered to be as an example of convergencebetween the 5G technology and the IoT technology.

Meanwhile, there have been various studies on system acquisition, beamfailure recovery, and cell reselection in 5G communication systemrecently.

The above information is presented as background information only toassist with an understanding of the disclosure. No determination hasbeen made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

Aspects of the disclosure are to address at least the above-mentionedproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the disclosure is to providea communication method and system for converging a fifth generation (5G)communication system for supporting higher data rates beyond a fourthgeneration (4G).

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

In accordance with an embodiment of the disclosure, a method comprises:transmitting, to a base station, a request for system information (SI);receiving, from the base station, an acknowledgement for the request;receiving a physical downlink control channel (PDCCH) addressed to a SIradio network temporary identifier (RNTI) in a first SI window for a SImessage immediately after receiving the acknowledgement; and receivingthe SI message, wherein receiving of a PDCCH is performed in a second SIwindow which is next to the first SI window in a modification period, incase that the SI message is not received by an end of the first SIwindow.

In accordance with another embodiment of the disclosure, a methodcomprises: receiving, from a terminal, a request for system information(SI); transmitting, to the terminal, an acknowledgement for the request;and transmitting, to the terminal, a physical downlink control channel(PDCCH) addressed to a SI radio network temporary identifier (RNTI) in afirst SI window for a SI message, wherein the first SI window ismonitored by the terminal for the SI message immediately after receivingthe acknowledgement, and wherein the receiving of a PDCCH is performedin a second SI window which is next to the first SI window in amodification period, in case that the SI message is not transmitted tothe terminal by an end of the first SI window.

In accordance with another embodiment of the disclosure, a terminalcomprises: a transceiver configured to transmit and receive a signal;and a controller configured to: transmit, to a base station, a requestfor system information (SI), receive, from the base station, anacknowledgement for the request, receive a physical downlink controlchannel (PDCCH) addressed to a SI radio network temporary identifier(RNTI) in a first SI window for a SI message immediately after receivingthe acknowledgement, and receive the SI message, wherein receiving of aPDCCH is performed in a second SI window which is next to the first SIwindow in a modification period, in case that the SI message is notreceived by an end of the first SI window.

In accordance with another aspect of the disclosure, a base stationcomprises: a transceiver configured to transmit and receive a signal;and a controller configured to: receive, from a terminal, a request forsystem information (SI), transmit, to the terminal, an acknowledgementfor the request, and transmit, to the terminal, a physical downlinkcontrol channel (PDCCH) addressed to a SI radio network temporaryidentifier (RNTI) in a first SI window for a SI message, wherein thefirst SI window is monitored by the terminal for the SI messageimmediately after receiving the acknowledgement, and wherein receivingof a PDCCH is performed in a second SI window which is next to the firstSI window in a modification period, in case that the SI message is nottransmitted to the terminal by an end of the first SI window.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates an example of monitoring system information (SI)window according to an embodiment of the disclosure;

FIG. 2 illustrates another example of monitoring SI window according toan embodiment of the disclosure;

FIG. 3 illustrates another example of monitoring SI window according toan embodiment of the disclosure;

FIG. 4 illustrates another example of monitoring SI window according toan embodiment of the disclosure;

FIG. 5 illustrates another example of monitoring SI window according toan embodiment of the disclosure;

FIGS. 6A and 6B illustrate other examples of monitoring SI windowaccording to an embodiment of the disclosure;

FIG. 7 illustrates another example of monitoring SI window according toan embodiment of the disclosure;

FIG. 8 illustrates another example of monitoring SI window according toan embodiment of the disclosure;

FIG. 9 illustrates another example of monitoring SI window according toan embodiment of the disclosure;

FIG. 10 illustrates an example of performing a beam failure recoveryaccording to an embodiment of the disclosure;

FIG. 11 illustrates an example of performing a cell reselection while anon-demand SI request is ongoing according to an embodiment of thedisclosure;

FIG. 12 illustrates another example of performing a cell reselectionwhile an on-demand SI request is ongoing according to an embodiment ofthe disclosure;

FIG. 13 illustrates another example of performing a cell reselectionwhile an on-demand SI request is ongoing according to an embodiment ofthe disclosure;

FIG. 14 is a block diagram of a terminal according to an embodiment ofthe disclosure; and

FIG. 15 is a block diagram of a base station according to an embodimentof the disclosure.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thedisclosure. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of thedisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of thedisclosure is provided for illustration purpose only and not for thepurpose of limiting the disclosure as defined by the appended claims andtheir equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

It is known to those skilled in the art that blocks of a flowchart (orsequence diagram) and a combination of flowcharts may be represented andexecuted by computer program instructions. These computer programinstructions may be loaded on a processor of a general-purpose computer,special purpose computer, or programmable data processing equipment.When the loaded program instructions are executed by the processor, theycreate a means for carrying out functions described in the flowchart.Because the computer program instructions may be stored in a computerreadable memory that is usable in a specialized computer or aprogrammable data processing equipment, it is also possible to createarticles of manufacture that carry out functions described in theflowchart. Because the computer program instructions may be loaded on acomputer or a programmable data processing equipment, when executed asprocesses, they may carry out operations of functions described in theflowchart.

A block of a flowchart may correspond to a module, a segment, or a codecontaining one or more executable instructions implementing one or morelogical functions, or may correspond to a part thereof. In some cases,functions described by blocks may be executed in an order different fromthe listed order. For example, two blocks listed in sequence may beexecuted at the same time or executed in reverse order.

In this description, the words “unit”, “module” or the like may refer toa software component or hardware component, such as, for example, afield-programmable gate array (FPGA) or an application-specificintegrated circuit (ASIC) capable of carrying out a function or anoperation. However, a “unit”, or the like, is not limited to hardware orsoftware. A unit, or the like, may be configured so as to reside in anaddressable storage medium or to drive one or more processors. Units, orthe like, may refer to software components, object-oriented softwarecomponents, class components, task components, processes, functions,attributes, procedures, subroutines, program code segments, drivers,firmware, microcode, circuits, data, databases, data structures, tables,arrays or variables. A function provided by a component and unit may bea combination of smaller components and units, and may be combined withothers to compose larger components and units. Components and units maybe configured to drive a device or one or more processors in a securemultimedia card.

Prior to the detailed description, terms or definitions necessary tounderstand the disclosure are described. However, these terms should beconstrued in a non-limiting way.

The “base station (BS)” is an entity communicating with a user equipment(UE) and may be referred to as BS, base transceiver station (BTS), nodeB (NB), evolved NB (eNB), access point (AP), 5G NB (5GNB), or gNB.

The “UE” is an entity communicating with a BS and may be referred to asUE, device, mobile station (MS), mobile equipment (ME), or terminal.

In the recent years several broadband wireless technologies have beendeveloped to meet the growing number of broadband subscribers and toprovide more and better applications and services. The second generationwireless communication system has been developed to provide voiceservices while ensuring the mobility of users. Third generation wirelesscommunication system supports not only the voice service but also dataservice. In recent years, the fourth wireless communication system hasbeen developed to provide high-speed data service. However, currently,the fourth generation wireless communication system suffers from lack ofresources to meet the growing demand for high speed data services. Thus,a fifth generation wireless communication system is being developed tomeet the growing demand for high speed data services, supportultra-reliability and low latency applications.

The fifth generation wireless communication system will be implementednot only in lower frequency bands but also in higher frequency (mmWave)bands, e.g., 10 GHz to 100 GHz bands, so as to accomplish higher datarates. To mitigate propagation loss of the radio waves and increase thetransmission distance, the beamforming, massive Multiple-InputMultiple-Output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna,an analog beam forming, large scale antenna techniques are beingconsidered in the design of fifth generation wireless communicationsystem. In addition, the fifth generation wireless communication systemis expected to address different use cases having quite differentrequirements in terms of data rate, latency, reliability, mobility etc.However, it is expected that the design of the air-interface of thefifth generation wireless communication system would be flexible enoughto serve the UEs having quite different capabilities depending on theuse case and market segment the UE cater service to the end customer.

Example use cases the fifth generation wireless communication systemwireless system are expected to address is enhanced Mobile Broadband(eMBB), massive Machine Type Communication (m-MTC), ultra-reliable lowlatency communication (URLLC) etc. The eMBB requirements like tens ofGbps data rate, low latency, high mobility so on and so forth addressthe market segment representing the wireless broadband subscribersneeding internet connectivity everywhere according to the related art,all the time and on the go. The m-MTC requirements like very highconnection density, infrequent data transmission, very long batterylife, low mobility address so on and so forth address the market segmentrepresenting the Internet of Things (IoT)/Internet of Everything (IoE)envisioning connectivity of billions of devices. The URLL requirementslike very low latency, very high reliability and variable mobility so onand so forth address the market segment representing the Industrialautomation application, vehicle-to-vehicle/vehicle-to-infrastructurecommunication foreseen as one of the enablers for autonomous cars.

Embodiment 1—On-Demand SI Acquisition

FIG. 1 illustrates an example of monitoring system information (SI)window according to an embodiment of the disclosure.

In fifth generation (also referred as NR or New Radio) wirelesscommunication system, system information is divided into minimum SI(comprising of master information block (MIB) and system informationblock 1 (SIB1)) and other SI (SIB 2, SIB 3 and so on). SIBs other thanSIB1 are carried in SystemInformation (SI) messages, which aretransmitted on the downlink shared channel (DL-SCH). SIBs having thesame periodicity can be mapped to the same SI message. Each SI messageis transmitted within periodically occurring time domain windows(referred to as SI-windows with same length for all SI messages). EachSI message is associated with a SI-window and the SI-windows ofdifferent SI messages do not overlap. That is, within one SI-window onlythe corresponding SI message is transmitted. The scheduling informationin SIB 1 includes mapping between SIBs and SI messages, periodicity ofeach SI message and SI window length. The scheduling information in SIB1 includes an indicator for each SI message, which indicates whether theconcerned SI message is being broadcasted or not. If at least one SImessage is not being broadcasted, SIB1 may include random accessresources (physical random access channel (PRACH) preamble(s) and PRACHresource/occasion(s)) for requesting gNB to broadcast one or more SImessage(s). gNB can signal random access resources for each SI messagewhich is not being broadcasted. Alternately gNB can signal random accessresources which are common for all SI messages which are not beingbroadcasted.

If UE requires an SI message to operate in cell and that SI message isnot being broadcasted, the UE shall:

-   -   If SIB1 received from gNB includes information on random access        resources (PRACH preamble(s) and PRACH resource(s)) for        requesting SI, UE (i.e., radio resource control (RRC) layer)        initiates the Random Access procedure using the PRACH        preamble(s) and PRACH resource(s) the SI message which UE wants        to request and waits for acknowledgement for SI request from a        lower layer (i.e., medium access control (MAC) layer). If        acknowledgement for the SI request is received from lower layer,        UE monitors the SI window of the requested SI message in one or        more SI period(s) of that SI message.

During the random access procedure, UE transmits Msg1 (i.e., Randomaccess preamble) using the random access resources corresponding to theSI message which UE wants to request Upon receiving the Msg1, based onreceived preamble and PRACH occasion in which preamble is received, gNBidentifies that Msg1 is a SI request and it transmits SI requestacknowledgement. SI request acknowledgement is included in random accessresponse (also referred as Msg2). For SI request acknowledgement theMsg2 MAC protocol data unit (PDU) includes a MAC subPDU having a MACsubheader only and this MAC subheader includes random access preambleidentifier (RAPID) of received preamble. After transmitting Msg1, UEwaits for Msg2 corresponding to the transmitted random access preamblein a response window. Upon receiving Msg2 wherein the Msg2 includes aMAC subPDU having a MAC subheader only and this MAC subheader includesRAPID of transmitted preamble, acknowledgement for the SI request isconsidered to be received by the UE (i.e., MAC layer) and then MAC layerinforms RRC that SI request acknowledgement is received.

-   -   If SIB1 received from gNB does not include information on random        access resources (PRACH preamble(s) and PRACH resource(s)) for        requesting SI, UE initiates transmission ofRRCSystemInfoRequest        message (i.e., RRC message) and waits for acknowledgement for SI        request (i.e., RRCSystemInfoRequest message) from lower layer        (i.e., MAC). If acknowledgement for SI request (i.e.,        RRCSystemInfoRequest message) is received from lower layer, UE        monitors the SI window of the requested SI message in one or        more SI period(s) of that SI message.

During the random access procedure, UE transmits Msg1 (i.e., Randomaccess preamble) and waits for random access response (also referred asMsg2) corresponding to the transmitted random access preamble. Randomaccess response (also referred as Msg2) corresponding to the transmittedrandom access preamble is considered successfully received by UE if Msg2includes a MAC subPDU having a MAC subheader and payload (i.e., MAC RAR)where MAC subheader includes the RAPID of the transmitted random accesspreamble. MAC RAR includes uplink (UL) grant, TA, TC-RNTI. In the ULgrant received in successfully received random access response (Msg2),UE transmits Msg3. Msg3 includes common control channel (CCCH) SDUwherein the CCCH SDU includes RRCSystemInfoRequest message. Aftertransmitting the Msg3, UE waits for Msg4 including the contentionresolution identity which matches the first 48 bits of CCCH SDUtransmitted in Msg3. If UE receives such Msg4 after transmitting theCCCH SDU including RRCSystemInfoRequest message, acknowledgement for theSI request is considered to be received by the UE (i.e., MAC layer) andMAC layer informs RRC that SI request acknowledgement is received.

The issue with above procedure is that UE is not aware of the SIperiod(s) in which requested SI message will be transmitted after UEreceives acknowledgement for SI request. UE unnecessarily monitoring SIwindows of requested SI message in several SI periods leads to a powerconsumption of the UE. In the standardization discussion it was proposedthat after receiving the SI request ack, UE monitors up to ‘W’ SIperiods (100), where a value of the ‘W’ is signaled by gNB. W SI periodsstart from earliest SI period which starts at least X ms further awayfrom the instant in which acknowledgment for SI request is received. Theissue with this approach is that it requires signaling of the additionalparameter ‘W’. Signaling of additional parameter increases the signalingoverhead of SIB 1.

Hereinafter, various embodiments according to the disclosure areexplained in detail.

Embodiment 1-1

FIGS. 2, 3, and 4 illustrate other examples of monitoring SI windowaccording to various embodiments of the disclosure.

If SIB1 received from gNB includes information on random accessresources (PRACH preamble(s) and PRACH resource(s)) for requesting SI,UE initiates the Random Access procedure using the PRACH preamble(s) andPRACH resource(s) indicated by the information in the SI message (210).For example, UE transmits Msg1 (i.e., Random access preamble) to the gNBand waits for acknowledgement for SI request. To overcome the abovementioned issue, it is proposed that after receiving acknowledgment forSI request (220), UE determines the SI window(s) to monitor as follows:

-   -   After receiving acknowledgment for SI request in modification        period N (230):    -   if there is at least one remaining SI Window of the requested SI        message in modification period N, UE monitors the SI window(s)        of the requested SI message in the modification period N (240,        300). This procedure is also illustrated in FIG. 3. Meanwhile, a        modification period is defined as follows:

The modification period is configured by system information. Themodification period boundaries are defined by SFN values for which SFNmod m=0, where m is the number of radio frames comprising themodification period. For a SI message, location of SI windows aredetermined as follows: the SI-window starts at the slot # a, where a=xmod N, in the radio frame for which SFN mod T=FLOOR(x/N), where T is theperiodicity of the concerned SI message and N is the number of slots ina radio frame, x is equal to (n−1)*w, w is the SI window length, n isthe index of SI message in list of SI messages in SIB 1.

-   -   Otherwise, i.e., if there is no remaining SI window of the        request SI message in modification period N (250, 410), UE        monitors the SI window(s) of the requested SI message in the        modification period N+1 (250, 420). This procedure is also        illustrated in FIG. 4.

FIG. 5 illustrates another example of monitoring SI window according toan embodiment of the disclosure.

If SIB1 received from gNB does not include information on random accessresources (PRACH preamble(s) and PRACH resource(s)) for requesting SI,UE initiates a transmission of RRCSystemInfoRequest message to the gNB.UE transmits Msg1 (i.e., Random access preamble) and waits for randomaccess response (510, 520). In the UL grant received in the receivedrandom access response, UE transmits RRCSystemInfoRequest message (i.e.,Msg3) and waits for acknowledgement for the Msg3 which is a SI request(i.e., RRCSystemInfoRequest message) (530, 540). To overcome the issue,it is proposed that after receiving acknowledgment for SI request (550),UE determines the SI window(s) to monitor as follows:

-   -   After receiving acknowledgment for SI request in modification        period N:    -   if there is at least one remaining SI Window of the requested SI        message in modification period N, UE monitors the SI window(s)        of the requested SI message in the modification period N (560,        300). This procedure is also illustrated in the above described        FIG. 3.    -   Otherwise, i.e., if there is no remaining SI window of the        request SI message in modification period N (570, 410), UE        monitors the SI window(s) of the requested SI message in the        modification period N+1 (570, 420). This procedure is also        illustrated in the above described FIG. 4.

It is to be noted that procedure explained in FIGS. 3 and 4 can also beused upon receiving acknowledgment for SI request wherein SI request istransmitted to gNB using dedicated RRC signaling message whereinRRCSystemInfoRequest is transmitted in dedicated UL grant. In this caseSI request acknowledgement can be a RRC message or RRC Reconfigurationmessage. FIGS. 3 and 4 can also be used upon receiving acknowledgmentfor SI request wherein SI request is transmitted to gNB in MsgA of 2step contention based random access procedure. In two step CBRA, firstmessage (i.e., MsgA) consists of random access preamble transmitted onPRACH occasion and MAC PDU transmitted in a physical uplink sharedchannel (PUSCH) occasion. MAC PDU includes CCCH SDU which includesRRCSystemInfoRequest. In response to MsgA UE receives MsgB. In this caseSI request acknowledgment is MsgB. MsgB including the contentionresolution identity which matches the first 48 bits of CCCH SDUtransmitted in MsgA is considered as SI request acknowledgment.

FIGS. 6A and 6B illustrate other examples of monitoring SI windowaccording to an embodiment of the disclosure.

Referring to FIG. 6A, if SIB1 broadcasted from gNB includes informationon random access resources (PRACH preamble(s) and PRACH resource(s)) forrequesting SI, UE initiates the Random Access procedure using the PRACHpreamble(s) and PRACH resource(s) indicated by the information in the SImessage (605). For example, UE transmits Msg1 (i.e., Random accesspreamble) to the gNB and waits for acknowledgement for SI request (610).

Referring to FIG. 6B, if SIB1 broadcasted from gNB does not includeinformation on random access resources (PRACH preamble(s) and PRACHresource(s)) for requesting SI, UE initiates a transmission ofRRCSystemInfoRequest message to the gNB. UE transmits Msg1 (i.e., Randomaccess preamble) and waits for random access response (625, 630). In theUL grant received in the received random access response, UE transmitsRRCSystemInfoRequest message (i.e., Msg3) and waits for acknowledgementfor the Msg3 which is a SI request (i.e., RRCSystemInfoRequest message)(635, 640).

Referring to FIG. 6A or 6B, after receiving the acknowledgement for SIrequest, for acquiring the requested SI message, UE shall receive thephysical downlink control channel (PDCCH) containing a scheduling radionetwork temporary identifier (RNTI), i.e., system information RNTI(SI-RNTI). That is, the UE monitors the PDCCH by decoding the PDCCH withthe SI-RNTI, from the start of the first SI-window after receivingacknowledgment for SI request and continues until the end of theSI-window whose absolute length in time is given by si-WindowLength, oruntil the SI message was received (615, 645).

If the SI message was not received by the end of the SI-window and ifthe UE has not yet monitored all the SI-window occasions in the currentmodification period, the UE repeats reception at the next SI-windowoccasion for the concerned SI message in the current modification period(620, 650).

FIG. 7 illustrates another example of monitoring SI window according toan embodiment of the disclosure.

An acknowledgement for SI request is received by the UE (710). Afterreceiving the acknowledgement for SI request, for acquiring therequested SI message, UE shall receive the PDCCH containing a schedulingRNTI, i.e., SI-RNTI. That is, the UE monitors the PDCCH by decoding thePDCCH with the SI-RNTI. The UE monitors the PDCCH from the start of thefirst SI-window after receiving acknowledgment for SI request andcontinues until the end of the SI-window whose absolute length in timeis given by si-WindowLength, or until the SI message was received (720).In other words, immediately after receiving acknowledgment for SIrequest the UE monitors the PDCCH from the start of the SI-window andcontinues until the end of the SI-window whose absolute length in timeis given by si-WindowLength, or until the SI message was received (720).

If the SI message was received, the UE determines that SI messagereception is successfully completed (730, 740). On the other hand, ifthe SI message was not received by the end of the SI-window and thereare more SI window occasions left in current modification period (750),the UE repeats reception at the next SI window occasion for theconcerned SI message in the current modification period (770). If thereare no more SI window occasions left in current modification period(750), the UE determines that SI message reception is not successful andmay resend the SI request (760).

It is to be noted that procedure explained in FIGS. 6 and 7 can also beused upon receiving acknowledgment for SI request wherein SI request istransmitted to gNB using dedicated RRC signaling message whereinRRCSystemInfoRequest is transmitted in dedicated UL grant. In this caseSI request acknowledgement can be a RRC message or RRC Reconfigurationmessage. FIGS. 6 and 7 can also be used upon receiving acknowledgmentfor SI request wherein SI request is transmitted to gNB in MsgA of 2step contention based random access procedure. In two step CBRA, firstmessage (i.e., MsgA) consists of random access preamble transmitted onPRACH occasion and MAC PDU transmitted in PUSCH occasion. MAC PDUincludes CCCH SDU which includes RRCSystemInfoRequest. In response toMsgA UE receives MsgB. In this case SI request acknowledgment is MsgB.MsgB including the contention resolution identity which matches thefirst 48 bits of CCCH SDU transmitted in MsgA is considered as SIrequest acknowledgment.

Hereinafter, operations of gNB according to the embodiments aredescribed.

-   -   After transmitting acknowledgment for SI request to the UE in        modification period N:    -   if there is at least one remaining SI Window of the requested SI        message in modification period N, gNB transmits requested SI        message in SI window(s) of the requested SI message in the        modification period N.    -   Otherwise, gNB transmits requested SI message in SI window(s) of        the requested SI message in the modification period N+1.

In another embodiment, after transmitting the acknowledgement for SIrequest gNB transmits the requested SI message in SI window(s) of thecurrent modification period i.e., the modification period in whichacknowledgement for SI request is sent.

Embodiment 1-2

FIGS. 8 and 9 illustrate other examples of monitoring SI windowaccording to various embodiments of the disclosure.

In another embodiment of the disclosure, it is proposed that afterreceiving acknowledgment for SI request, UE determines the SI window(s)to monitor as follows:

-   -   After receiving acknowledgment for SI request in modification        period N (910):    -   UE monitors the SI window(s) of the requested SI message in the        modification period N and N+1. This procedure is illustrated in        FIG. 8, 9. After receiving the acknowledgement for SI request in        modification period N (910), for acquiring the requested SI        message, UE shall receive the PDCCH containing a scheduling        RNTI, i.e., SI-RNTI. That is, the UE monitors the PDCCH by        decoding the PDCCH with the SI-RNTI. The UE monitors the PDCCH        from the start of the first SI-window after receiving        acknowledgment for SI request and continues until the end of the        SI-window, or until the SI message was received (920).    -   If the SI message was received, the UE determines that SI        message reception is successfully completed (930, 940). On the        other hand, if the SI message was not received by the end of the        SI-window of modification period N or N+1 and there are more SI        window occasions left in the modification period N or N+1 (950),        the UE repeats reception at the next SI window occasion for the        concerned SI message in the modification period N or N+1 (970).        This procedure is also illustrated in FIG. 8, e.g., 810, 820. If        there are no more SI window occasions left in the modification        period N or N+1 (950), the UE determines that SI message        reception is not successful and may resend the SI request (960).

Hereinafter, operations of gNB according to the embodiments aredescribed. * After transmitting acknowledgment for SI request to the UEin modification period N:

-   -   gNB transmits requested SI message in SI window(s) of the        requested SI message in the modification period N and N+1.

It is to be noted that procedure explained in FIGS. 8 and 9 can also beused upon receiving acknowledgment for SI request wherein SI request istransmitted to gNB using dedicated RRC signaling message whereinRRCSystemInfoRequest is transmitted in dedicated UL grant. In this case,SI request acknowledgement can be a RRC message or RRC Reconfigurationmessage. FIGS. 8 and 9 can also be used upon receiving acknowledgmentfor SI request wherein SI request is transmitted to gNB in MsgA of 2step contention based random access procedure. In two step CBRA, firstmessage (i.e., MsgA) consists of random access preamble transmitted onPRACH occasion and MAC PDU transmitted in PUSCH occasion. MAC PDUincludes CCCH SDU which includes RRCSystemInfoRequest. In response toMsgA UE receives MsgB. In this case SI request acknowledgment is MsgB.MsgB including the contention resolution identity which matches thefirst 48 bits of CCCH SDU transmitted in MsgA is considered as SIrequest acknowledgment.

Embodiment 1-3

In another embodiment of the disclosure, it is proposed that afterreceiving acknowledgment for SI request, UE determines the SI window(s)to monitor as follows:

-   -   After receiving acknowledgment for SI request in modification        period N:    -   if there are at least ‘X’ remaining SI Window of the requested        SI message in modification period N, UE monitors the SI        window(s) of the requested SI message in the modification period        N.    -   Otherwise, UE monitors the SI window(s) of the requested SI        message in the modification period N and N+1.

Hereinafter, operations of gNB according to the embodiments aredescribed.

-   -   After transmitting acknowledgment for SI request in modification        period N:    -   if there are at least ‘X’ remaining SI Window of the requested        SI message in modification period N, gNB transmits requested SI        message in SI window(s) of the requested SI message in the        modification period N.    -   Otherwise, gNB transmits requested SI message in SI window(s) of        the requested SI message in the modification period N and N+1

It is to be noted that procedure explained in above embodiments (1-1,1-2 and 1-3) can also be used upon receiving acknowledgment for SIrequest wherein SI request is transmitted to gNB using dedicated RRCsignaling message wherein RRCSystemInfoRequest is transmitted indedicated UL grant. In this case SI request acknowledgement can be a RRCmessage or RRC Reconfiguration message. embodiments (1-1, 1-2 and 1-3)can also be used upon receiving acknowledgment for SI request wherein SIrequest is transmitted to gNB in MsgA of 2 step contention based randomaccess procedure. In two step CBRA, first message (i.e., MsgA) consistsof random access preamble transmitted on PRACH occasion and MAC PDUtransmitted in PUSCH occasion. MAC PDU includes CCCH SDU which includesRRCSystemInfoRequest. In response to MsgA UE receives MsgB. In this caseSI request acknowledgment is MsgB. MsgB including the contentionresolution identity which matches the first 48 bits of CCCH SDUtransmitted in MsgA is considered as SI request acknowledgment.

Embodiment 2—Beam Failure Recovery

In a beamformed system, beam failure recovery procedure is used torecover beam upon beam failure detection. The UE may be configured byradio resource control (RRC) signaling with a beam failure recoveryprocedure. The beam failure recovery procedure is used for indicating tothe serving gNB of a new synchronization signal block (SSB) or channelstate information reference signal (CSI-RS) when beam failure isdetected on the serving SSB(s)/CSI-RS(s). Beam failure is detected bythe UE by counting beam failure instance indication. The UE operationfor beam failure detection and recovery in 5G system is as follows:

If beam failure instance is detected: UE start or restart thebeamFailureDetectionTimer and increment BFI_COUNTER by 1.

-   -   if BFI_COUNTER>=beamFailureInstanceMaxCount:    -   if beamFailureRecoveryConfig is configured:        -   start the beamFailureRecoveryTimer, if configured;        -   initiate a Random Access procedure on the SpCell (i.e.,            special cell including primary cell (PCell) and primary            secondary cell (pSCell)) by applying the parameters            powerRampingStep, preambleReceivedTargetPower, and            preambleTransMax configured in beamFailureRecoveryConfig.            -   During the random access procedure, if contention free                (CF) resources are configured in                beamFailureRecoveryConfig and criteria to select them is                met, select CF resources. Otherwise select contention                based (CB) resources.    -   else:        -   initiate a Random Access procedure on the SpCell.            -   During the random access procedure, CB random access                resources are selected.

If the Random Access procedure is successfully completed: stop thebeamFailureRecoveryTimer, if configured; and consider the Beam FailureRecovery procedure successfully completed.

In the fifth generation wireless communication system, bandwidthadaptation (BA) is supported. With BA, a UE's transmission bandwidth andreception bandwidth does not need to be as large as the bandwidth of thecell and can be adjusted as followings: the width of the bandwidth canbe ordered to change (e.g., to shrink during period of low activity tosave power); the location of the bandwidth can move in the frequencydomain (e.g., to increase scheduling flexibility); and the subcarrierspacing of the bandwidth can be ordered to change (e.g., to allowdifferent services). A subset of the total cell bandwidth of a cell isreferred to as a Bandwidth Part (BWP) and BA is achieved by configuringthe UE with at least one BWP(s) and telling the UE which of theconfigured BWPs is currently active. There is one active downlink (DL)BWP and one active uplink (UL) BWP. A Serving Cell (i.e., PCell orSCell) may be configured with one or more BWPs, and for an activatedserving cell, there is always one active DL BWP and one active UL BWP atany point in time.

In a cell, gNB periodically broadcasts SSBs (i.e., SS blocks). SSBcomprises primary synchronization signal (PSS), secondarysynchronization signal (SSS) and physical broadcast channel (PBCH). SSBsdo not occupy the full channel bandwidth. According to current design,if SSBs are not located within the BWP, contention based random access(CBRA) resources cannot be configured in that BWP. Additionally,contention free random access (CFRA) resources can be configured in aBWP only if CBRA resources are configured in that BWP. The consequenceof this design is that if SSBs are not located in active DL BWP, randomaccess channel (RACH) occasions cannot be configured in active UL BWPand hence CFRA cannot be used for beam failure recovery (BFR).

Embodiment 2-1

FIG. 10 illustrates an example of performing a beam failure recoveryaccording to an embodiment of the disclosure.

In an embodiment of the disclosure, we propose the following procedurefor initiating random access procedure for beam failure recovery. Notethat in below procedure, if PRACH occasions are not configured on activeUL BWP, UE will also switch to initial DL BWP and initial UL BWP.

-   -   Upon beam failure detection (i.e.,        BFI_COUNTER>=beamFailurelnstanceMaxCount) (1010):    -   if beamFailureRecoveryConfig is configured on active UL BWP        (1020); or    -   if PRACH occasions are not configured on active UL BWP and        beamFailureRecoveryConfig is configured on initial UL BWP        (1050):        -   start the beamFailureRecoveryTimer (1030, 1060);        -   initiate a Random Access procedure on the SpCell by applying            the parameters powerRampingStep,            preambleReceivedTargetPower, and preambleTransMax configured            in beamFailureRecoveryConfig (1040, 1070).        -   If CF resources are configured in beamFailureRecoveryConfig            and criteria (i.e., there is at least one SSB/CSI-RS amongst            SSBs/CSI-RSs for which CF resources are provided) with            reference signal received power (RSRP) above a threshold to            select them is met, select CF resources. Otherwise select CB            resources    -   else (1020, 1050):        -   initiate a Random Access procedure on the SpCell by applying            the parameters powerRampingStep,            preambleReceivedTargetPower, and preambleTransMax configured            in rachConfigCommon (1080)

Note: During the random access procedure, CB random access resources areselected

Embodiment 2-2

In this embodiment of the disclosure, if PRACH occasions are notconfigured in active UL BWP, BWP configuration of active UL BWP mayinclude the BWP ID (beamFailureRecoveryBWPId) of the BWP where the BFRshould be initiated upon beam failure detection. The detail procedure isas follows:

-   -   Upon beam failure detection (i.e.,        BFI_COUNTER>=beamFailurelnstanceMaxCount):    -   if beamFailureRecoveryConfig is configured on active UL BWP; or        -   if PRACH occasions are not configured on active BWP and            beamFailureRecoveryConfig is configured on BWP indicated by            beamFailureRecoveryBWPId:        -   start the beamFailureRecoveryTimer;        -   initiate a Random Access procedure on the SpCell by applying            the parameters powerRampingStep,            preambleReceivedTargetPower, and preambleTransMax configured            in beamFailureRecoveryConfig.        -   If CF resources are configured in beamFailureRecoveryConfig            and criteria (i.e., there is at least one SSB/CSI-RS amongst            SSBs/CSI-RSs for which CF resources are provided) with RSRP            above a threshold to select them is met, select CF            resources. Otherwise select CB resources    -   else:        -   initiate a Random Access procedure on the SpCell by applying            the parameters powerRampingStep,            preambleReceivedTargetPower, and preambleTransMax configured            in rachConfigCommon

Note: During the random access procedure, CB random access resources areselected

-   -   Upon initiation of the Random Access procedure on a Serving        Cell, the medium access control (MAC) entity shall for this        Serving Cell:    -   if PRACH occasions are not configured for the active UL BWP:        -   if the Random Access procedure is initiated for BFR and            beamFailureRecoveryConfig is configured on BWP indicated by            beamFailureRecoveryBWPId:        -   switch the active UL BWP to BWP indicated by            beamFailureRecoveryBWPId;        -   switch the active DL BWP to BWP indicated by            beamFailureRecoveryBWPId        -   else:        -   switch the active UL BWP to BWP indicated by            initialUplinkBWP;        -   if the Serving Cell is a SpCell:        -   switch the active DL BWP to BWP indicated by            initialDownlinkBWP.

Embodiment 2-3

In this embodiment of the disclosure, if PRACH occasions are notconfigured in active UL BWP, UE performs beam failure recovery on BWPwhich includes reference signals (RSs) which are quasi-collocated(QCLed) with RSs in active DL BWP. The QCL relation can be signaled bygNB. The detail procedure is as follows:

-   -   Upon beam failure detection (i.e.,        BFI_COUNTER>=beamFailurelnstanceMaxCount):    -   if beamFailureRecoveryConfig is configured on active UL BWP; or    -   if PRACH occasions are not configured on active BWP and        beamFailureRecoveryConfig is configured on BWP which includes        RSs which are QCLed with RSs in active BWP:        -   start the beamFailureRecoveryTimer;        -   initiate a Random Access procedure on the SpCell by applying            the parameters powerRampingStep,            preambleReceivedTargetPower, and preambleTransMax configured            in beamFailureRecoveryConfig.        -   If CF resources are configured in beamFailureRecoveryConfig            and criteria (i.e., there is at least one SSB/CSI-RS amongst            SSBs/CSI-RSs for which CF resources are provided) with RSRP            above a threshold to select them is met, select CF            resources. Otherwise select CB resources    -   else:        -   initiate a Random Access procedure on the SpCell by applying            the parameters powerRampingStep,            preambleReceivedTargetPower, and preambleTransMax configured            in rachConfigCommon

Note: During the random access procedure, CB random access resources areselected

-   -   Upon initiation of the Random Access procedure on a Serving        Cell, the MAC entity shall for this Serving Cell:    -   if PRACH occasions are not configured for the active UL BWP:        -   if the Random Access procedure is initiated for BFR and            beamFailureRecoveryConfig is configured on BWP which            includes RSs which are QCLed with RSs in active BWP:            -   switch the active UL BWP to BWP indicated by                beamFailureRecoveryBWPId;            -   switch the active DL BWP to BWP indicated by                beamFailureRecoveryBWPId    -   else:        -   switch the active UL BWP to BWP indicated by            initialUplinkBWP;        -   if the Serving Cell is a SpCell:            -   switch the active DL BWP to BWP indicated by                initialDownlinkBWP.

Embodiment 3—Cell Reselection while On-Demand SI Request is Ongoing

FIGS. 11, 12, and 13 illustrate examples of performing a cellreselection while an on-demand SI request is ongoing according tovarious embodiments of the disclosure.

RRC initiates RA procedure for Msg1 based SI Request or RRC initiatestransmission of RRCSystemInfoRequest message (i.e., Msg3 based SIrequest or MsgA based SI request). RRC is waiting for acknowledgment forSI request and Cell reselection occurs during the waiting. In thisscenario, based on current procedure, ongoing RA procedure will continueon the reselected cell using the random access resources of previouscell. This is not desired behavior and will affect the random accessoperation of other UEs in reselected cell. This will also causeinterference in reselected cell.

MAC Handling: It would be sufficient to just reset the MAC in abovescenario. There is no need to release the MAC configuration. If MACconfiguration is released, INACTIVE UEs may be impacted (MACconfiguration in AS context may be wrongly discarded).

radio link control (RLC) Handling: After the RRC initiates transmissionof RRCSystemInformationRequest, RRCSystemInformationRequest message isdelivered to RLC transparent mode (TM) entity buffer. If cellreselection occurs before the MAC has received random access response(RAR), RRCSystemInformationRequest message in RLC buffer should bediscarded. Otherwise this may be wrongly transmitted later (e.g., whenconnection is established or resumed) after cell reselection.

So, in an embodiment the disclosure, if cell reselection occurs whilethe UE is waiting for acknowledgment for SI request (orRRCSystemInfoRequest), UE shall reset MAC. In other words, afterinitiating Msg1 based SI Request by receiving random access resourcesfrom SIB 1 (1110, 1120 in FIG. 11), or after initiating transmission ofRRCSystemInfoRequest message by determining that SIB1 does not includerandom access resources (1210, 1220, 1230, 1240 in FIG. 12), or afterinitiating 2 step RA for SI request when 2 step CBRA is triggered for SIrequest (1310, 1320 in FIG. 13), if cell reselection occurs before theUE receives acknowledgment for SI request (or RRCSystemInfoRequest)(1130, 1250, 1330), UE shall reset MAC. The detailed operation aftercell reselection is explained in embodiments below.

Embodiment 3-1

1. Cell reselection occurs during ongoing random access procedure (i.e.,random access procedure can be 2 step random access procedure or 4 steprandom access procedure)

A. If the random access procedure is ongoing for RRC setup (i.e., timerT300 is running), perform the 1st set of operations

i. 1st set of operations

1) reset MAC;

2) stop all timers that are running except T320 and T325;

3) discard any stored AS context, fullI-RNTI, shortI-RNTI-Value,ran-PagingCycle and ran-NotificationAreaInfo;

4) discard the AS security context including the K_(RRcenc) key, theK_(RRcint), the K_(UPint) key and the K_(UPenc) key, if stored;

5) release all radio resources, including release of the RLC entity, theMAC configuration and the associated packet data convergence protocol(PDCP) entity and service data adaptation protocol (SDAP) for allestablished radio bearers (RBs);

6) indicate the release of the RRC connection to upper layers togetherwith the release cause set to connection failure;

7) enter RRC IDLE and perform procedures as specified in TS 38.304;

B. If the random access procedure is ongoing for RRC resume (i.e., timer319 is running), perform the 2nd set of operations

i) 2nd set of operations

1) set the variable pendingRnaUpdate to ‘FALSE’, if that is set to TRUE;

2) reset MAC;

3) stop all timers that are running except T320 and T325;

4) discard any stored AS context, fullI-RNTI, shortI-RNTI-Value,ran-PagingCycle and ran-NotificationAreaInfo;

5) discard the AS security context including the K_(RRcenc) key, theK_(RRcint), the K_(UPint) key and the K_(UPenc) key, if stored;

6) release all radio resources, including release of the RLC entity, theMAC configuration and the associated PDCP entity and SDAP for allestablished RBs;

7) indicate the release of the RRC connection to upper layers togetherwith the release cause set to resume failure;

8) enter RRC IDLE and perform procedures as specified in TS 38.304;

C. If the random access procedure is ongoing for SI request (i.e., RRCis waiting for SI request ack), perform the 3rd set of operations

i. 3rd set of operations

1) reset MAC;

2) RLC handling: as described in embodiments below

Embodiment 3-2

The UE shall:

1>if cell reselection occurs while waiting for the acknowledgment for SIrequest or RRCSystemInfoRequest:

2>reset MAC, release the MAC configuration and re-establish RLC for allRBs that are established;

This may only be applied to UE in idle state.

Embodiment 3-3

The UE shall:

1>if cell reselection occurs while waiting for the acknowledgment for SIrequest or RRCSystemInfoRequest message:

2>reset MAC, release the MAC configuration;

2>if waiting for the acknowledgment of RRCSystemInfoRequest message

3>re-establish RLC for all RBs that are established;

This may only be applied to UE in idle state.

Embodiment 3-4

The UE shall:

1>if cell reselection occurs while waiting for the acknowledgment for SIrequest or RRCSystemInfoRequest message:

2>reset MAC;

2>if waiting for the acknowledgment of RRCSystemInfoRequest message:

3>release the RLC entity and the associated PDCP entity and SDAP for allestablished RBs;

OR

The UE shall:

1>if cell reselection occurs while waiting for the acknowledgment for SIrequest or RRCSystemInfoRequest message:

2>reset MAC;

2>if waiting for the acknowledgment of RRCSystemInfoRequest message:

3>release RLC entity for SRB 0 or discard all contents in RLC entity forSRB 0;

OR

The UE shall:

1>if cell reselection occurs while waiting for the acknowledgment for SIrequest or RRCSystemInfoRequest message:

2>reset MAC;

2>if waiting for the acknowledgment of RRCSystemInfoRequest message:

3>release the RLC entity and the associated PDCP entity and SDAP for SRB0;

OR

The UE shall:

1>if cell reselection occurs while waiting for the acknowledgment for SIrequest or RRCSystemInfoRequest message:

2>reset MAC;

2>release the RLC entity and the associated PDCP entity and SDAP for allestablished RBs;

OR

The UE shall:

1>if cell reselection occurs while waiting for the acknowledgment for SIrequest or RRCSystemInfoRequest message:

2>reset MAC;

2>release RLC entity for SRB 0 or discard all contents in RLC entity forSRB 0;

OR

The UE shall:

1>if cell reselection occurs while waiting for the acknowledgment for SIrequest or RRCSystemInfoRequest message:

2>reset MAC;

2>release the RLC entity and the associated PDCP entity and SDAP for SRB0;

This may only be applied to UE in idle state.

In all embodiments about if UE is in idle state, MAC configuration mayalso be released.

FIG. 14 is a block diagram of a terminal according to an embodiment ofthe disclosure.

Referring to FIG. 14, a terminal includes a transceiver 1410, acontroller 1420 and a memory 1430. The transceiver 1410, the controller1420 and the memory 1430 are configured to perform the operations of theUE illustrated in the figures, e.g., FIGS. 1 to 13, or described above.Although the transceiver 1410, the controller 1420 and the memory 1430are shown as separate entities, they may be realized as a single entitylike a single chip. Or, the transceiver 1410, the controller 1420 andthe memory 1430 may be electrically connected to or coupled with eachother.

The transceiver 1410 may transmit and receive signals to and from othernetwork entities, e.g., a BS.

The controller 1420 may control the UE to perform functions according toone of the embodiments described above. The controller 1420 may refer toa circuitry, an ASIC, or at least one processor.

In an embodiment, the operations of the terminal may be implementedusing the memory 1430 storing corresponding program codes. Specifically,the terminal may be equipped with the memory 1430 to store program codesimplementing desired operations. To perform the desired operations, thecontroller 1420 may read and execute the program codes stored in thememory 1430 by using a processor or a central processing unit (CPU).

FIG. 15 is a block diagram of a BS according to an embodiment of thedisclosure.

Referring to FIG. 15, a BS includes a transceiver 1510, a controller1520 and a memory 1530. The transceiver 1510, the controller 1520 andthe memory 1530 are configured to perform the operations of the network(e.g., gNB) illustrated in the figures, e.g., FIGS. 1 to 13, ordescribed above. Although the transceiver 1510, the controller 1520 andthe memory 1530 are shown as separate entities, they may be realized asa single entity like a single chip. The transceiver 1510, the controller1520 and the memory 1530 may be electrically connected to or coupledwith each other.

The transceiver 1510 may transmit and receive signals to and from othernetwork entities, e.g., a terminal.

The controller 1520 may control the BS to perform functions according toone of the embodiments described above. The controller 1520 may refer toa circuitry, an ASIC, or at least one processor.

In an embodiment, the operations of the BS may be implemented using thememory 1530 storing corresponding program codes. Specifically, the BSmay be equipped with the memory 1530 to store program codes implementingdesired operations. To perform the desired operations, the controller1520 may read and execute the program codes stored in the memory 1530 byusing a processor or a CPU.

As described above, embodiments disclosed in the specification anddrawings are merely used to specific examples to easily explain thecontents of the disclosure and to help understanding, but are notintended to limit the scope of the disclosure. Accordingly, the scope ofthe disclosure should be analyzed to include all changes ormodifications derived based on the technical concept of the disclosurein addition to the embodiments disclosed herein.

While the disclosure has been shown and described with reference tovarious embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the disclosure as definedby the appended claims and their equivalents

What is claimed is:
 1. A method of receiving system information by aterminal in a wireless communication system, the method comprising:transmitting, to a base station, a request for system information (SI);receiving, from the base station, an acknowledgement for the request;receiving a physical downlink control channel (PDCCH) addressed to a SIradio network temporary identifier (RNTI) in a first SI window for a SImessage immediately after receiving the acknowledgement; and receivingthe SI message, wherein receiving of a PDCCH is performed in a second SIwindow which is next to the first SI window in a modification period, incase that the SI message is not received by an end of the first SIwindow.
 2. The method of claim 1, wherein the first SI window ismonitored from a start of the first SI window until the end of the firstSI window or until the SI message is received, and wherein an absolutelength in time of the first SI window is configured by the base station.3. The method of claim 2, wherein the modification period is amodification period in which the acknowledgement for the request isreceived from the base station.
 4. The method of claim 1, wherein thetransmitting of the request includes initiating a random accessprocedure by using a physical random access channel (PRACH) preamble anda PRACH resource, in case that a system information block 1 (SIB1)includes information associated with the PRACH preamble and the PRACHresource, and wherein the transmitting of the request includestransmitting a radio resource control (RRC) message for requestingsystem information, in case that the SIB1 does not include theinformation associated with the PRACH preamble and the PRACH resource.5. The method of claim 1, further comprising: detecting that a cellreselection is occurred while the terminal is waiting for theacknowledgement for the request; resetting a medium access control(MAC); and releasing a radio link control (RLC) entity for signalingradio bearer 0 (SRB0), in case that the request is based on a RRCmessage for requesting system information.
 6. A method of transmittingsystem information by a base station in a wireless communication system,the method comprising: receiving, from a terminal, a request for systeminformation (SI); transmitting, to the terminal, an acknowledgement forthe request; and transmitting, to the terminal, a physical downlinkcontrol channel (PDCCH) addressed to a SI radio network temporaryidentifier (RNTI) in a first SI window for a SI message, wherein thefirst SI window is monitored by the terminal for the SI messageimmediately after receiving the acknowledgement, and wherein receivingof a PDCCH is performed in a second SI window which is next to the firstSI window in a modification period, in case that the SI message is nottransmitted to the terminal by an end of the first SI window.
 7. Themethod of claim 6, wherein the first SI window is monitored by theterminal from a start of the first SI window until the end of the firstSI window or until the SI message is transmitted to the terminal, andwherein an absolute length in time of the first SI window is configuredby the base station.
 8. The method of claim 7, wherein the modificationperiod is a modification period in which the acknowledgement for therequest is received from the base station.
 9. The method of claim 6,wherein the receiving of the request includes initiating a random accessprocedure by using a physical random access channel (PRACH) preamble anda PRACH resource, in case that a system information block 1 (SIB1)includes information associated with the PRACH preamble and the PRACHresource, and wherein the receiving of the request includes receiving aradio resource control (RRC) message for requesting system information,in case that the SIB1 does not include the information associated withthe PRACH preamble and the PRACH resource.
 10. The method of claim 6,wherein an occurrence of a cell reselection is detected by the terminalwhile waiting for the acknowledgement for the request, wherein a mediumaccess control (MAC) is reset by the terminal, and wherein a radio linkcontrol (RLC) entity for signaling radio bearer 0 (SRB0) is released bythe terminal, in case that the request is based on a RRC message forrequesting system information.
 11. A terminal of receiving systeminformation in a wireless communication system, the terminal comprising:a transceiver configured to transmit and receive a signal; and acontroller configured to: transmit, to a base station, a request forsystem information (SI), receive, from the base station, anacknowledgement for the request, receive a physical downlink controlchannel (PDCCH) addressed to a SI radio network temporary identifier(RNTI) in a first SI window for a SI message immediately after receivingthe acknowledgement, and receive the SI message, wherein receiving of aPDCCH is performed in a second SI window which is next to the first SIwindow in a modification period, in case that the SI message is notreceived by an end of the first SI window.
 12. The terminal of claim 11,wherein the first SI window is monitored from a start of the first SIwindow until the end of the first SI window or until the SI message isreceived, and wherein an absolute length in time of the first SI windowis configured by the base station.
 13. The terminal of claim 12, whereinthe modification period is a modification period in which theacknowledgement for the request is received from the base station. 14.The terminal of claim 11, wherein the transmitting of the requestincludes initiating a random access procedure by using a physical randomaccess channel (PRACH) preamble and a PRACH resource, in case that asystem information block 1 (SIB1) includes information associated withthe PRACH preamble and the PRACH resource, and wherein the transmittingof the request includes transmitting a radio resource control (RRC)message for requesting system information, in case that the SIB1 doesnot include the information associated with the PRACH preamble and thePRACH resource.
 15. The terminal of claim 11, wherein the controller isfurther configured to: detect that a cell reselection is occurred whilethe terminal is waiting for the acknowledgement for the request, reset amedium access control (MAC), and release a radio link control (RLC)entity for signaling radio bearer 0 (SRB0), in case that the request isbased on a RRC message for requesting system information.
 16. A basestation of transmitting system information in a wireless communicationsystem, the base station comprising: a transceiver configured totransmit and receive a signal; and a controller configured to: receive,from a terminal, a request for system information (SI), transmit, to theterminal, an acknowledgement for the request, and transmit, to theterminal, a physical downlink control channel (PDCCH) addressed to a SIradio network temporary identifier (RNTI) in a first SI window for a SImessage, wherein the first SI window is monitored by the terminal forthe SI message immediately after receiving the acknowledgement, andwherein receiving of a PDCCH is performed in a second SI window which isnext to the first SI window in a modification period, in case that theSI message is not transmitted to the terminal by an end of the first SIwindow.
 17. The base station of claim 16, wherein the first SI window ismonitored by the terminal from a start of the first SI window until theend of the first SI window or until the SI message is transmitted to theterminal, and wherein an absolute length in time of the first SI windowis configured by the base station.
 18. The base station of claim 17,wherein the modification period is a modification period in which theacknowledgement for the request is received from the base station. 19.The base station of claim 16, wherein the receiving of the requestincludes initiating a random access procedure by using a physical randomaccess channel (PRACH) preamble and a PRACH resource, in case that asystem information block 1 (SIB1) includes information associated withthe PRACH preamble and the PRACH resource, and wherein the receiving ofthe request includes receiving a radio resource control (RRC) messagefor requesting system information, in case that the SIB1 does notinclude the information associated with the PRACH preamble and the PRACHresource.
 20. The base station of claim 16, wherein an occurrence of acell reselection is detected by the terminal while waiting for theacknowledgement for the request, wherein a medium access control (MAC)is reset by the terminal, and wherein a radio link control (RLC) entityfor signaling radio bearer 0 (SRB0) is released by the terminal, in casethat the request is based on a RRC message for requesting systeminformation.